Calculator inputs
The page stays in one main content column, while the calculator fields flow into 3, 2, and 1 columns by screen size.
Plotly graph
The graph compares air and vacuum wavelengths across your selected range. The diagonal line shows where both values would be equal.
Example data table
These sample values illustrate standard-air conversion behavior with a precise inverse calculation.
| Air wavelength (nm) | Vacuum wavelength (nm) | Shift (nm) | Typical use |
|---|---|---|---|
| 200.000000 | 200.064749 | 0.064749 | Near-UV boundary checks |
| 400.000000 | 400.113102 | 0.113102 | Visible spectroscopy setup |
| 500.000000 | 500.139485 | 0.139485 | General optics reference |
| 632.800000 | 632.974989 | 0.174989 | Laser calibration example |
| 700.000000 | 700.193062 | 0.193062 | Red and near-IR work |
Formula used
The calculator converts air wavelength to vacuum wavelength by multiplying the air value by the refractive index of standard air. For iterative mode, the refractive index is updated until the vacuum value stabilizes.
λvac = λair × n
σ² = (1 / λµm)²
n = 1 + 0.05792105 / (238.0185 − σ²) + 0.00167917 / (57.362 − σ²)
n = 1 + 0.05791817 / (238.0185 − σ²) + 0.00167909 / (57.362 − σ²)
n = 1 + 0.000064328 + 0.0294981 / (146 − σ²) + 0.00025540 / (41 − σ²)
n = 1 + 0.0000834254 + 0.02406147 / (130 − σ²) + 0.00015998 / (38.9 − σ²)
How to use this calculator
- Enter the wavelength measured in air.
- Select the unit you want for both input and output.
- Choose a refractive index method and an inverse scheme.
- Set CO₂, precision, iterations, and decimal places when needed.
- Optionally paste several air wavelengths into the batch box.
- Pick a graph range to visualize the conversion trend.
- Press Convert wavelength to display results above the form.
- Export the result table with the CSV or PDF buttons.
Frequently asked questions
1) Why is the vacuum wavelength always slightly larger?
Light travels more slowly in air than in vacuum. Frequency stays the same, so wavelength in vacuum becomes slightly longer after conversion.
2) Which method should I choose first?
Ciddor 1996 is a practical default for many precision optics and spectroscopy workflows. It also lets you adjust the CO₂ concentration.
3) What does the iterative inverse option do?
It starts with the air wavelength, estimates the vacuum value, recomputes refractive index from that estimate, and repeats until the change becomes smaller than your chosen precision target.
4) When is direct inversion useful?
Direct inversion is very fast and works well for interactive calculations. It is helpful when you want quick checks across many wavelengths.
5) What is the Piskunov analytical inverse option?
It uses a closed-form air-to-vacuum relation often associated with VALD-style conversion tools. It avoids repeated iterations while staying very practical for spectroscopy tables.
6) Should I convert wavelengths below 200 nm?
Usually, no. Deep-UV measurements are commonly reported directly in vacuum, so an air conversion is often unnecessary in that range.
7) Why include a batch input area?
Batch conversion saves time when you have a line list, teaching dataset, or calibration set. It also produces a ready-to-export results table.
8) What does the graph show?
The graph plots air wavelengths against the converted vacuum wavelengths. The separation from the diagonal reveals how the optical shift grows across your chosen range.